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Fix multi-register costs in BasicTTI::getCastInstrCost

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For an cast (extension, etc.), the currently logic predicts a low cost if the
associated operation (keyed on the destination type) is legal (or promoted).
This is not true when the number of values required to legalize the type is
changing. For example, <8 x i16> being sign extended by <8 x i32> is not
generically cheap on PPC with VSX, even though sign extension to v4i32 is
legal, because two output v4i32 values are required compared to the single
v8i16 input value, and without custom logic in the target, this conversion will
scalarize.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205487 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel
2014-04-02 23:18:54 +00:00
parent a18ad697a9
commit 9263e6f08d
2 changed files with 23 additions and 1 deletions
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3
lib/CodeGen/BasicTargetTransformInfo.cpp
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@ -297,7 +297,8 @@ unsigned BasicTTI::getCastInstrCost(unsigned Opcode, Type *Dst,
return 0;
// If the cast is marked as legal (or promote) then assume low cost.
if (TLI->isOperationLegalOrPromote(ISD, DstLT.second))
if (SrcLT.first == DstLT.first &&
TLI->isOperationLegalOrPromote(ISD, DstLT.second))
return 1;
// Handle scalar conversions.